We studied the long term flux distribution of Cygnus X-1 using RXTE-ASM lightcurves in two energy bands B (3-5 keV) & C (5-12.1 keV) as well as MAXI lightcurves in energy bands B (4–10 keV) & C (10–20 keV). The flux histograms were fitted using a two component model. For MAXI data, each of the components is better fitted by a log-normal distribution, rather than a Gaussian one. Their best fit centroids and fraction of time the source spends being in that component are consistent with those of the Hard and Soft spectral states Thus, the long term flux distribution of the states of Cygnus X-1 has a log-normal nature which is the same as that found earlier for much shorter time-scales. For RXTE-ASM data, one component corresponding approximately to the Hard state is better represented by a log-normal but for the other one a Gaussian is preferred and whose centroid is not consistent with the Soft state. This discrepancy, could be due to the larger fraction of the Intermediate state (∼11.25%) in the RXTE-ASM data as compared to the MAXI one (∼4%). Fitting the flux distribution with three components did not provide an improvement for either RXTE-ASM or MAXI data, suggesting that the data corresponding to the Intermediate state may not represent a separate spectral state, but rather represent transitions between the two states.

我们使用两个能带 B (3-5 keV) 和 C (5-12.1 keV) 中的 RXTE-ASM 光曲线以及能带 B (4-10 keV) 中的 MAXI 光曲线研究了 Cygnus X-1 的长期通量分布) & C (10–20 keV)。通量直方图使用两分量模型拟合。对于 MAXI 数据，每个分量都更适合采用对数正态分布，而不是高斯分布。它们的最佳拟合质心和源在该分量中花费的时间部分与硬和软光谱状态的一致 因此，天鹅座 X-1 状态的长期通量分布具有对数正态性质，即与之前在更短的时间尺度上发现的相同。对于 RXTE-ASM 数据，一个近似对应于 Hard 状态的分量最好用对数正态表示，但对于另一个，高斯是首选，其质心与 Soft 状态不一致。这种差异可能是由于 RXTE-ASM 数据中的中间态 (~11.25%) 与 MAXI one (~4%) 相比更大。用三个分量拟合通量分布并没有为 RXTE-ASM 或 MAXI 数据提供改进，这表明对应于中间状态的数据可能不代表单独的光谱状态，而是代表两个状态之间的转换。